1. Field of the Invention
The present invention relates to a disk drive, and more particularly to a disk drive suppressing a jerky motion of a lens holder upon alignment of light beams irradiating a disk.
2. Description of the Background Art
In a disk drive for a compact disk (CD), a mini disk (MD) or the like, an objective lens is used to collect light beams on a disk surface to form a spot. A mechanism for reducing the spot size is provided, since a smaller spot size enables higher-density recording of information on the disk. Specifically, the mechanism causes the light beams from an optical pick-up to impinge on the disk surface in a right angle to prevent coma.
A disk has tracks on which information is recorded. Tracking of a track is conducted, as is well known, by disk rotation by rotation of a turntable, and by movement of an optical pick-up along a guide shaft. A disk suffers bend, eccentricity and others, hindering accurate tracking of an information-recorded position on the disk only in the above-described manner. There is a need for an adjustment mechanism which can track the information-recorded position accurately to read the information therefrom even if the position is displaced due to an unexpected external factor.
The objective lens is fixed to a lens holder. The lens holder is supported by a lens holder supporting portion which moves along the guide shaft. The lens holder is provided with a slide hole, and the lens holder supporting portion is provided with a slide shaft. The lens holder is supported by the lens holder supporting portion with the slide shaft penetrating the slide hole.
In the above-described adjustment mechanism in a conventional device, the lens holder is made to move in a direction along which the slide shaft extends, to make the light beams focused on a spot. The lens holder is also made rotatable about the slide shaft, for two-dimensional alignment of the tracks. Specifically, a magnetically driven portion for focusing and a magnetically driven portion for tracking are provided between the lens holder and the lens holder supporting portion. The magnetically driven portions for focusing and for tracking constitute the above-described adjustment mechanism. Normally, focusing and tracking coils are mounted on the lens holder side, and focusing and tracking permanent magnets are arranged on the lens holder supporting portion side opposite to the coils.
When a current is passed through the focusing coil, the lens holder is driven up and down along the slide shaft by magnetic force, and thus, focusing adjustment of the objective lens attached to the lens holder is carried out. Similarly, when a current is passed through the tracking coil, the lens holder is rotated about the slide shaft by magnetic force, so that tracking adjustment is carried out. Provision of the mechanisms both for focusing adjustment and tracking adjustment makes it possible, even if the information-recorded position is displaced by any external factor, to deal with the displacement of the spot position from the track to accomplish accurate tracking of the track position.
It however is necessary to provide a prescribed clearance between the slide hole of the lens holder and the slide shaft of the lens holder supporting portion, which clearance causes the lens holder to jerkily shift when it moves for the adjustment as described above. Once the jerky motion occurs, the quality of the information, and hence, the performance as the information reproduction device would be degraded. To prevent such a jerky motion due to the clearance, means for applying side or lateral pressure has been proposed, which presses the sidewall of the slide hole of the lens holder against the slide shaft. With this means, however, problems have been pointed out that high working accuracy is required and that friction between the slide shaft and the slide hole causes vibrations and the like. Thus, there has been proposed, to solve the problems, to maintain a contact position between the slide shaft and the slide hole at a specific position (e.g., Japanese Patent Laying-Open Nos. 2000-20986 and 2002-74711).
In the conventional disk drive shown in FIG. 9, magnetic pieces 154 are arranged on both ends of a center line L of a lens holder 104 to which an objective lens 110 is attached. Magnetic force between magnetic pieces 154 and permanent magnets 151, 152 opposite to the respective magnetic pieces produces lateral pressure M against lens holder 104. A slide shaft 103 and a slide hole 141 are brought into contact with each other at a portion 143 of a rim of slide hole 141 in contact with center line L. This contact point 143 is made to match the center of gravity G of lens holder 104. In a normal operation, the slide hole and the slide shaft come into contact with each other at contact point 143. Thus, contact point 143 also functions as the center H of rotation driving force resulting from the force generated between tracking permanent magnets 151, 152 and tracking coils 153. As such, maintaining the contact point at a specific position prevents vibrations from occurring and ensures smooth and high-precision adjustment.
To make the slide shaft and the slide hole contact at a prescribed position, however, it is necessary to increase the working accuracy of the lens holder and also increase the accuracy in positioning of the permanent magnets. In view of the foregoing, there has been a demand for development of a disk drive suppressing the jerky motion of a lens holder attributable to the clearance between the slide hole and the slide shaft with a simple mechanism.